The present invention relates to the texturing of magnetic data storage media, and more particularly to surface treatments applied to media substrates to modify the results of subsequent laser texturing.
Laser texturing of magnetic disks, particularly over areas designed for contact with data transducing heads, is known to reduce friction and improve wear characteristics as compared to mechanically textured disks. Traditional laser texturing involves focusing a laser beam onto a disk substrate surface at multiple locations, forming at each location a depression surrounded by a raised rim as disclosed in U.S. Pat. No. 5,062,021 (Ranjan) and U.S. Pat. No. 5,108,781 (Ranjan). An alternative, as disclosed in International Publications No. WO 97/07931 and No. WO 97/43079, is to use a laser beam to form domes or nodules (also called bumps) rather than rims. The texturing features can have either circular or elliptical profiles.
Collectively, the texturing features form a texture pattern that provides a desired surface roughness throughout the transducing head contact zone. A particularly preferred pattern is a spiral, formed by rotating the substrate disk at a controlled angular speed while moving a laser radially with respect to the disk. The laser is pulsed to form the individual texturing features. Although this approach has been highly successful in terms of reducing dynamic friction and improving the wear characteristics of dedicated transducing head contact zones, the texturing features, whether rims or nodules, tend to vary as to their height, i.e., the outward projection from a nominal surface plane of the transducing head contact zone. The desirable range of feature heights is limited, at the low end by the need to avoid stiction. The maximum feature heights are limited by the desired glide height, i.e. the distance of a transducing head from the nominal surface plane when supported aerodynamically due to disk rotation. As glide heights are reduced, the variance among feature heights becomes more of a problem.
The reduced transducing head glide heights or flying heights also raise the need for texturing features with reduced heights, to avoid turbulence in the air bearing and minimize the risk of unintended head/disk contact when the data transducing head is near the contact zone. This has motivated designers to reduce the heights of the laser texturing features, which also may involve reducing the diameters of the features. To maintain the stability of texturing features, it would be desirable to reduce the feature heights without the proportional reduction in their diameters.
Therefore, it is an object of the present invention to provide a laser textured magnetic data storage medium in which the texturing features, whether rims or nodules, are more uniform in height throughout the transducing head contact zone.
Another object is to provide a magnetic data storage medium substrate with surface characteristics selectively altered to enhance the results of subsequent laser texturing by improving uniformity of texturing feature heights, improving feature diameter-to-height ratios, or both.
A further object of the invention is to provide a process for controllably altering surface properties of magnetic disk substrates to improve the surface topography produced by subsequent laser texturing.
Yet another object is to provide a magnetic data reading and storage apparatus in which more uniform texturing features with reduced heights, preferably without corresponding reductions in their diameters, permit lower transducing head glide heights.